Much attention has been directed to the development of materials having improved barrier properties with respect to e.g. contaminants. In the field of packing a variety of materials are used. Especially materials comprising polymeric or thermoplastic compounds are widespread and used in the form of e.g. films, coatings, semi-rigid or rigid sheets or containers.
Improving barrier properties, especially organic vapor barrier properties is an important goal for manufacturers of materials. One main field of application is in the provision of plastic-based materials used to package e.g. food products including liquid and solid products, products which should be protected from the entry of harmful substances or products emitting flavoring substances or harmful and/or undesired volatiles over their storage lives.
Mobile or volatile, organic contaminant material or substances can derive from the environment, but also from the material as for example from a printing chemical, a coating chemical or from any contaminant in recycled material and can of course derive from the product to be wrapped or packaged. A permeant, contaminant or volatile in the meaning of the present invention is a substance that can exist in the atmosphere at a substantial detectable concentration and can be transmitted through a known material. A large variety of permeants or volatiles are known.
A problem known for a long time relates to materials or containers for temporarily storing soiled diapers, incontinent products, medical dressings, sanitary napkins, etc. Especially the temporary storage of soiled disposable or washable diapers prior to final disposal or laundering represents a long-felt problem. The malodours emanating from soiled diapers are highly undesirable.
Usually soiled diapers are stored in a lockable container or resealable garbage bag, which is e.g. placed in the nursery, before transporting them to an outdoor storage vessel. It is widespread to use plastic diaper pails having a tight lid for the temporary storage of the soiled diapers. Said bags or diaper pails reduce the release of the unpleasant odours when sealed. However, the barrier properties of e.g. thermoplastic garbage bags known in the art are limited and are not satisfactory.
Moreover, upon opening the bag or container, the malodours escape into the area giving an extremely unpleasant sensation to the person attempting to place another soiled diaper into the same. Also, especially diaper pails tend to retain the malodours even after the diapers have been removed. In other words, the plastic materials commonly used for the manufacture of such bags or diaper pails tend to temporarily adsorb the odours or volatile substances emitting from the diapers. Accordingly, the garbage bag or container by itself becomes a source of malodours regardless whether diapers are contained or not.
Similar problems are observed with respect to the diapers itself, since they usually may have very efficient moisture absorbing properties but show no or very low barrier properties with respect to the unpleasant odours emitting from a soiled diaper. Accordingly, a prior art problem is in the inability to provide a suitable construction that would keep moisture away from the surface of the diaper which comes into contact with the infant's skin and avoids at least partly the release of smelling volatile substances.
Disposable diapers have met with increased commercial acceptance in recent years and many different constructions have been proposed and used. Usually, the moisture absorbing functions are accomplished by a multilayer diaper comprising a fibrous facing layer which is to be brought into contact with the infant's skin, a layer of an absorbing material as for example a highly porous, loosely compacted cellulosic material and a moisture-impervious backing sheet.
The facing layer often is made of a porous material and its fibers have less wetability for water than the fibers of the absorbing material, resulting in a tendency for liquid to flow from the facing layer into the absorbing unit. Liquid which might pass through the absorbing unit during discharge (when flow is rapid) is held back by an impervious backing sheet or film for sufficient time to permit absorption to take place. However, the outer or backing layer does not prevent volatile substances or odours from permeating through said layer.
The problems indicated above with respect to soiled diapers apply to the same extent to other materials or containers e.g. for temporarily storing incontinent products, medical dressings, sanitary napkins or any other article emitting volatile substances. Similar problems also relate to materials or containers for storing drinks or food. Ideally, the materials or containers should prevent any substances which would affect aroma or taste of the content of the containers from adulterating the food or drink in the container. Moreover, it is clear that the barrier material should not have or release odour of its own which it can impart to the contents of the container or package. Changes of the taste of the container's contents are often due to light-induced aroma changes.
Especially gable-top cartons and plastic bottles are widespread in the food packaging industry. Liquid-packaging carton stock (paperboard) is typically coated on both sides with polyethylene. For food carton applications, the food product contact polymer (e.g., LDPE and LLDPE, and occasionally HDPE) is extrusion-coated onto the paperboard. The extrusion coating can be a single extrusion layer. Modern gable-top cartons retain the simple carton geometry but include technology refinements acquired over 60 years of development and commercial use. Today, the carton can have a plurality of layers specially engineered comprising an inner barrier layer of amorphous nylon or EVOH and outer layers of heat sealable olefin polymers. LDPE is frequently used as the product contact layer due to its excellent sealing properties, low-cost and minimal off-flavor contribution.
Serious problems relate to materials or containers for storing dairy products since they have a characteristic smooth, bland taste and soft flavor, so that the presence of an off-flavor or off-odor is readily noticeable. Light-induced off-flavors make milk products less acceptable to consumers. Clear plastic milk bottles, and to a lesser extent gable-top polyethylene coated paperboard cartons, in the presence of light and naturally occurring riboflavin or cysteine react with oxygen to form a series of sulfur containing compounds (methyl mercaptan, hydrogen sulfide, dimethyl sulfide and dimethyl disulfide).
In WO 97/33044 the use of cyclodextrin in rigid or semi-rigid cellulosic sheets is disclosed. The cyclodextrin acts as a barrier or a trap for contaminants. The barrier properties of the material disclosed in WO 97/33044 are based on entrapment of the respective permeants in the internal hydrophobic space of the cyclodextrin molecule. The cyclodextrin material is generally used in the form of a compatible, derivatized cyclodextrin. According to WO 97/33044 the preferred cyclodextrin is a derivatized cyclodextrin having at least one substituent group bonded to the cyclodextrin molecule.
Moreover, it is known from WO 97/30122 that the barrier properties of a thermoplastic polymer can be improved by forming a barrier layer with a dispersed compatible cyclodextrin derivative in the polymer.
WO 93/10174 is directed to thermoplastic films containing one or more metal powders selected from aluminium powder, magnesium powder, zinc powder and manganese powder. The application is directed to a thermoplastic film which is characterized in that the film comprises at least 0.1 wt. %, preferably 0.5 to 6 wt. %, based on the total weight of the mixture of thermoplastic and filler, of at least one metal powder, selected from the group consisting of aluminium powder, magnesium powder, manganese powder and mixtures thereof. According to WO 93/10174 the average particle size of the metal powders is in the range of 5-20 μm
In none of the aforementioned documents of the prior art, barrier materials containing modified cyclodextrin in combination with another reactive or trapping substance incorporated into a corresponding barrier material are disclosed.